The toners used for electrophotography, electrostatic recording, electrostatic printing or the like are conventionally produced by fusing and kneading a toner binder such as a styrene type resin or a polyester together with a colorant, followed by pulverizing the resulting mixture.
These toners are developed on a support member such as paper and thereafter fused under heat by using a heat roll to thereby fix them. In this case, if the temperature of the heat roll is too high, the toner is fused excessively, giving rise to the problem that the toner is deposited on the heat roll (hot offset). On the other hand, if the temperature of the heat roll is excessively low, the toner is insufficiently fused, giving rise to the problem that the toner is fixed unsatisfactorily. From necessities for energy savings and the miniaturization of devices, there have been the demands for toners which produce the hot offset at higher temperatures (hot offset resistance) and have lower fixing temperature (low temperature fixing ability).
It is also required for these toners to have storage stability under heat so that they are not made into a block at the ambient temperature kept in a device during storage.
Since the glossiness of an image is demanded of the toner especially in a full color system, it is necessary for a molten toner to have low viscosity. The fulfillment of the demand results in easy production of the hot offset. To be free from the hot offset, silicon oil has been applied to the heat roll in a full color system.
Such a method of applying silicone oil to the heat roll, however, requires an oil applicator rendering the entire system complicated and large and causing the heat roll to deteriorate, requiring maintenance at intervals of a fixed period of time. Also, the oil adheres to copying papers, OHP (overhead projectors) films or the like inevitably, posing the problem of impaired color tones.
While, in recent years, there have been increasing needs of toners with a small particle size to produce a high quality image and to improve the resolution. However, because a conventional kneaded and pulverized toner has an undefined shape, it has only insufficient fluidity when it is small-sized and hence it is difficult to supply the toner to a developing unit and the transferability is impaired.
(1) Toners using, as a toner binder, a polyester which is partially crosslinked using a polyfunctional monomer (Japanese Patent Application Laid-Open (JP-A) No. S57-109825) and (2) toners using, as a toner binder, a urethane-modified polyester (Japanese Patent Publication (JP-B) No. H7-101318) are proposed as those satisfying the storage stability under heat, low temperature fixing ability and hot offset resistance among the aforementioned requirements.
(3) Toners for a full color system which are produced by granulating polyester microparticles and wax microparticles are disclosed for the purpose of reducing the amount of oil to be applied to the heat roll (JP-A No. H7-56390).
Disclosed also are (4) polymerized toners synthesized by dispersing a vinyl monomer composition containing a colorant, a polar resin and a releasing agent in water followed by suspension-polymerization (JP-A No. 9-43909) and (5) toners globed by treating a toner comprising a polyester type resin in water by using a solvent (JP-A No. 9-34167) for the purpose of improving the powder fluidity and the transferability when the toner is small-sized.
The toners (1) to (3) disclosed, however, have insufficient powder fluidity and transferability and hence never give a high quality image when they are small-sized.
The disclosed toners (1) and (2) insufficiently satisfy the storage stability under heat and the low temperature fixing ability compatibly and cannot be used in a full color system because of no development of glossiness. The disclosed toner (3) insufficiently satisfies the low temperature fixing ability and the hot offset resistance in an oilless fixing condition.
The toners (4) and (5) are found to have an effect of improving the powder fluidity and the transferability. However, the toner (4) is insufficiently improved in the low temperature fixing ability, posing the problem that the energy required for fixing is increased. Especially, full color toners offers the same problem conspicuously. The toner (5), though it is superior to the toner (4) in the low temperature fixing ability, has insufficient hot offset resistance, so that it cannot preclude the necessity of the application of oil to the heat roll in a full color system.
An object of the present invention is to provide a toner which is superior in the powder fluidity and the transferability when it is small-sized and in all of the storage stability under heat, low temperature fixing ability and hot offset resistance.
A further object of the present invention to provide a toner which has high image glossiness, when it is used, for example, in a full color copying machine, and omits the application of oil to a heat roll.